Body fat often gets a bad rap, but it serves an important purpose. Your body stores the fat from the foods you eat in deposits that can be used for energy, insulation, and protection. Everyone needs some fat to live and function. When too much body fat accumulates, however, it can lead to obesity and obesity-related diseases, like type 2 diabetes and heart disease.

Figuring out how much body fat you have isn’t necessarily as easy as looking in a mirror or stepping on a scale. A bodybuilder and an obese person may be the same weight, but they have very different body fat percentages. Your weight alone cannot tell you much muscle or fat you have. Instead, you’ll need to determine your body fat percentage.

Read on to learn six different methods you can use to identify your body fat percentage.

A basic way to measure body fat percentage is by using a soft tape measure, like the kind you’d use for sewing, to record measurements of different parts of the body. You can also find tape measures specifically marketed as body fat tape measures, like these ones on Amazon. For this method, you’ll also need to know your height in inches.

In men

If you’re a man, measure the circumference of your neck and abdomen. Make sure you measure the largest part of each area. It may be easier to have a friend or family member help.

To calculate body fat percentage, subtract your neck value from your abdomen value to determine your circumference value. Look up this number on a body fat chart and compare it against your height to estimate your body fat percentage.

In women

If you’re a woman, you should record a measurement of the circumference of your neck, natural waist, and hips. Remember to measure each area at the widest part. You may want to ask a friend or family member to help.

To calculate body fat percentage, add your waist and hip measurements, and then subtract the neck measurement to determine your circumference value. For example, if your waist is 30, your hips are 36, and your neck is 13, your circumference value would be 53. Look up this number on a body fat chart and compare it against your height to estimate your body fat percentage.

Tips

When the tape is placed over the skin, it should make contact but not compress the skin in any way.

Take all measurements twice and average them. Then record to the nearest half inch.

If you can’t find the corresponding chart, you may consider using an online Navy Body Fat Calculator to obtain your estimated body fat percentage.

Accuracy

Taking measurements and plugging numbers into an online calculator is relatively easy, but this method isn’t necessarily the most accurate. There’s a lot of room for error when measuring yourself. Things like clothing, what you’ve eaten, and how tightly you pull the tape measure may also affect results.

A skin-fold test is done using a tool called calipers to pinch different areas of your body and measure body fat. There are a few ways to measure, but many people go with a three-site approach developed by researchers Jackson and Pollock in the 1980s. This method takes the least amount of time to complete. It’s also cost-effective, as you can find calipers online for less than $7.

How to:

If you’re a man, measure fat at your chest, abdominals, and thigh.

If you’re a woman, measure fat at your triceps, suprailiac (about an inch above the hip bone), and the thigh.

Calipers may come with instructions on how to convert these numbers to your body fat percentage.

Your bathroom scale may estimate your body fat as part of its various functions. Body fat scales use technology called bioelectrical impedance analysis (BIA). When you step on the scale, an electrical current passes through one leg, up to the pelvis, and down the other. Fat conducts far less electricity than the water and muscle you have in your body. So, when the scale picks up more resistance, it records more possible body fat.

Accuracy

These scales may not be as accurate as you’d like. Scale results may also vary wildly compared to results from other body fat percentage measurement methods. That’s because there are many variables at play that could affect results, including:

your hydration level

when you last exercised

when and what you last ate

Read your manual carefully, as some scales may be less accurate for older people, elite athletes, children, and people with osteoporosis.

Hydrodensitometry is a weighing method where you sit undressed in a chair that’s submerged in water. Your body density or weight under water is recorded as your body places a buoyant counterforce on the water and displaces it. The weight recorded can then be used to calculate your body fat percentage.

Underwater weighing for body fat percentage is highly accurate and considered the gold standard for measuring body fat percentage. The percentage that it estimates should be within 1 percent of body fat for both adults and children. It’s much more accurate than at-home methods, like skinfold and bioelectrical impedance.

You’ll need to go to a special facility to have your weight recorded this way. You also may not like having a test under water. And not all insurances cover the total cost of this type of test.

Another technique is air displacement plethysmography. After undressing, you enter a computerized, egg-shaped chamber (called a BOD POD) that totally encloses your body. Once your body density is determined through your weight and volume, the machine uses this data to calculate your body fat percentage.

Research has shown the BOD POD to be extremely accurate. It matches the accuracy of underwater measurement at within 1 percent of body fat for both adults and children.

This test must be done in a professional setting, and may or may not be covered by your health insurance.

Perhaps the most accurate method for determining body fat percentage is with magnetic resonance imaging (MRI) or computerized tomography (CT) scans. These machines take cross-sectional images of the body and can even measure intra-abdominal fat.

These tests are not often used for the sole purpose of measuring body fat. They are also very expensive.

If you have too little body fat, your body may not have enough energy to carry on with the day’s tasks. If you have too much body fat, you may increase your risk of developing hypertension, high cholesterol, diabetes, and heart disease.

Your BMI is your body mass index. This number is different from your body fat percentage because it simply tells you if you’re underweight, normal weight, overweight, or obese. It cannot tell you how much fat is on your body.

While useful in some situations and easy to calculate, your BMI may not be a very reliable indicator of your overall health. If you’re an athlete, for example, you may have a low body fat percentage, but due to all of your muscle, you may have a high BMI. BMI doesn’t take into account other important factors.

There are various ways to estimate body fat percentage, ranging from simple measurements to expensive tests. If you try several of these methods, you may receive different measures. Underwater weighing or tools like the BOD POD are the most accurate, but also the costliest unless insurance covers them.

Regardless of your body fat percentage, there are things you can do at home to maintain a healthy weight:

Make sure you get 150 minutes of moderate exercise (walking, cycling, water aerobics) or 75 minutes of vigorous exercise (running, swimming laps, playing sports) each week.

Carve out time for strength training two days a week. Try lifting weights, doing body-weight workouts, or doing yard work.